1. Field of the Invention
This invention is directed to an improved method of separating oil from biological material.
2. Description of Related Art
Many plants and plant-material, such as oil-seeds, cereal brans, beans, nuts, and microbial organisms, contain oils that can be useful for many commercial products. These oils are used in cooking, processing foods, cosmetics, lubricants, and a host of other useful products. Because of this high commercial demand, much work had been done in an attempt to improve oil extraction processes to make them more efficient and more suitable for mass extraction.
Numerous processes for the extraction of oil are known in the art. The most commonly used process is solvent extraction from a dried plant material. To use the conventional process, the plant material must already be dry. The plant material may be pretreated, for example, by flaking to facilitate penetration of the plant structure by a solvent, such as hexane, without creating fine particles. The dried, lipid-containing plant material is then contacted with the solvent that will dissolve the oil or other valuable lipids and extract them out of the material. Contact time is provided with the solvent typically by means of counter-current washing. The resulting mixture of solvent and lipid material (the miscella) is separated from the extracted plant material and fractionated to remove the solvent, leaving the lipid.
This process is problematic when applied to oil-containing microbial mass. To remove oils from the microbial biomass, the biomass must first be dried, e.g., by spray drying, then slurried in the solvent. Biomass is produced in a relatively dilute aqueous slurry (fermentation culture), which means drying is an expensive process. Additionally, the temperature profile during drying must be such that oil quality is not compromised. Conventional extract equipment, which rely on coarse screens to retain the oil-bearing material, is not designed to handle the particles produced by such means.
Second, the cells may need to be disrupted to permit adequate contact with the solvent. This cell disruption step generates a significant amount of fines which tend to be carried along with the product in the solvent. Consequently, before further processing, these fines must be removed by filtration, centrifugation, or a combination thereof. The fines clog equipment used in downstream processing steps and make extraction more difficult.
Third, the extracted biomass carries 10-50% hexane by weight with it. This hexane will contain some product, which is now lost. Additionally, the hexane must be substantially removed before the delipidated biomass can be disposed.
Extraction of oil from high moisture materials, including animal products, such as eggs, and microbial biomass, have been described using polar solvents that are partly or completely miscible with water (see, e.g., U.S. Pat. No. 5,112,956 to Tang, et al., and U.S. Pat. No. 5,539,133 to Kohn, et al.). In a separate and distinct technology, addition of polymers to water to create two immiscible phases, between which water soluble substances may be partitioned, are described in, e. g., U.S. Pat. No. 4,980,065 to Hsu. However, these processes are not fully satisfactory for efficient extraction of non-polar lipids, such as triglyceride oils, on a commercial scale.
Therefore, a need has arisen for a novel method of separating oil from biological material that overcomes the disadvantages and deficiencies of the prior art.